Beyond just sliding around the planet, the magnetic north and south poles have been known to completely flip as well; these reversals, recorded in the magnetism of ancient rocks, are unpredictable. The last one was 780,000 years ago. Are we overdue for another? No one knows.

Earth's Inconstant Magnetic Field12.29.03 Our planet's magnetic field is in a constant state of change, say researchers who are beginning to understand how it behaves and why.
Every few years, scientist Larry Newitt of the Geological Survey of Canada goes hunting. He grabs his gloves, parka, a fancy compass, hops on a plane and flies out over the Canadian arctic. Not much stirs among the scattered islands and sea ice, but Newitt's prey is there--always moving, shifting, elusive.

His quarry is Earth's north magnetic pole.

At the moment it's located in northern Canada, about 600 km from the nearest town: Resolute Bay, population 300, where a popular T-shirt reads "Resolute Bay isn't the end of the world, but you can see it from here." Newitt stops there for snacks and supplies--and refuge when the weather gets bad. "Which is often," he says.

Scientists have long known that the magnetic pole moves. James Ross located the pole for the first time in 1831 after an exhausting arctic journey during which his ship got stuck in the ice for four years. No one returned until the next century. In 1904, Roald Amundsen found the pole again and discovered that it had moved--at least 50 km since the days of Ross.

The pole kept going during the 20th century, north at an average speed of 10 km per year, lately accelerating "to 40 km per year," says Newitt. At this rate it will exit North America and reach Siberia in a few decades.

Keeping track of the north magnetic pole is Newitt's job. "We usually go out and check its location once every few years," he says. "We'll have to make more trips now that it is moving so quickly."

Earth's magnetic field is changing in other ways, too: Compass needles in Africa, for instance, are drifting about 1 degree per decade. And globally the magnetic field has weakened 10% since the 19th century. When this was mentioned by researchers at a recent meeting of the American Geophysical Union, many newspapers carried the story. A typical headline: "Is Earth's magnetic field collapsing?"

Probably not. As remarkable as these changes sound, "they're mild compared to what Earth's magnetic field has done in the past," says University of California professor Gary Glatzmaier.

Sometimes the field completely flips. The north and the south poles swap places. Such reversals, recorded in the magnetism of ancient rocks, are unpredictable. They come at irregular intervals averaging about 300,000 years; the last one was 780,000 years ago. Are we overdue for another? No one knows.

According to Glatzmaier, the ongoing 10% decline doesn't mean that a reversal is imminent. "The field is increasing or decreasing all the time," he says. "We know this from studies of the paleomagnetic record." Earth's present-day magnetic field is, in fact, much stronger than normal. The dipole moment, a measure of the intensity of the magnetic field, is now 8 x 1022 amps x m2. That's twice the million-year average of 4 x 1022 amps x m2.

To understand what's happening, says Glatzmaier, we have to take a trip ... to the center of the Earth where the magnetic field is produced.

At the heart of our planet lies a solid iron ball, about as hot as the surface of the sun. Researchers call it "the inner core." It's really a world within a world. The inner core is 70% as wide as the moon. It spins at its own rate, as much as 0.2o of longitude per year faster than the Earth above it, and it has its own ocean: a very deep layer of liquid iron known as "the outer core."
Right: a schematic diagram of Earth's interior. The outer core is the source of the geomagnetic field. [Larger image]

Earth's magnetic field comes from this ocean of iron, which is an electrically conducting fluid in constant motion. Sitting atop the hot inner core, the liquid outer core seethes and roils like water in a pan on a hot stove. The outer core also has "hurricanes"--whirlpools powered by the Coriolis forces of Earth's rotation. These complex motions generate our planet's magnetism through a process called the dynamo effect.

Using the equations of magnetohydrodynamics, a branch of physics dealing with conducting fluids and magnetic fields, Glatzmaier and colleague Paul Roberts have created a supercomputer model of Earth's interior. Their software heats the inner core, stirs the metallic ocean above it, then calculates the resulting magnetic field. They run their code for hundreds of thousands of simulated years and watch what happens.

What they see mimics the real Earth: The magnetic field waxes and wanes, poles drift and, occasionally, flip. Change is normal, they've learned. And no wonder. The source of the field, the outer core, is itself seething, swirling, turbulent. "It's chaotic down there," notes Glatzmaier. The changes we detect on our planet's surface are a sign of that inner chaos.

They've also learned what happens during a magnetic flip. Reversals take a few thousand years to complete, and during that time--contrary to popular belief--the magnetic field does not vanish. "It just gets more complicated," says Glatzmaier. Magnetic lines of force near Earth's surface become twisted and tangled, and magnetic poles pop up in unaccustomed places. A south magnetic pole might emerge over Africa, for instance, or a north pole over Tahiti. Weird. But it's still a planetary magnetic field, and it still protects us from space radiation and solar storms.

And, as a bonus, Tahiti could be a great place to see the Northern Lights. In such a time, Larry Newitt's job would be different. Instead of shivering in Resolute Bay, he could enjoy the warm South Pacific, hopping from island to island, hunting for magnetic poles while auroras danced overhead.

Sometimes, maybe, a little change can be a good thing.

lighthouse

February 11th, 2011, 05:10 AM

SOLAR TSUNAMI: Imagine a wave of hot plasma towering higher than Earth itself, rippling out from a central point in a circular pattern millions of kilometers in circumference. Researchers recently realized that such monster waves are real, and they happen routinely on the sun. Just yesterday, one of them surged over the western limb. Click on the image to view the shadowy yet staggering solar tsunami of Feb. 10th:

Movie credit: NASA's Solar Dynamics Observatory

The source of the wave was active sunspot 1153, currently located on the far side of the sun. An eruption in the sunspot's magnetic canopy propelled a shock wave across the stellar surface--all the way over the horizon where it could be seen from Earth. Sequences like this show how farside sunspots can actually "reach around" to affect the Earth-side of the sun. Suppose that wave ran into a magnetic filament , destabilized it, and triggered an explosion aimed at our planet. It's happened before. Imagine that.

Dec. 13, 2010: On August 1, 2010, an entire hemisphere of the sun erupted. Filaments of magnetism snapped and exploded, shock waves raced across the stellar surface, billion-ton clouds of hot gas billowed into space. Astronomers knew they had witnessed something big.

It was so big, it may have shattered old ideas about solar activity.

"The August 1st event really opened our eyes," says Karel Schrijver of Lockheed Martin's Solar and Astrophysics Lab in Palo Alto, CA. "We see that solar storms can be global events, playing out on scales we scarcely imagined before."

IMPACT! A CME hit Earth's magnetic field at approximately 0100 UT on Feb. 18th (8:00 pm EST on Feb. 17th). The impact was not as strong as expected considering the cloud's X-class origin. Nevertheless, geomagnetic storms are possible in the hours ahead. High-latitude sky watchers should be alert for auroras.

A powerful solar eruption that triggered a huge geomagnetic storm has disturbed radio communications and could disrupt electrical power grids, radio and satellite communication in the next days, NASA said.
A strong wave of charged plasma particles emanating from the Jupiter-sized sun spot, the most powerful seen in four years, has already disrupted radio communication in southern China.

The Class X flash -- the largest such category -- erupted at 0156 GMT Tuesday, according to the US space agency.

"X-class flares are the most powerful of all solar events that can trigger radio blackouts and long-lasting radiation storms," disturbing telecommunications and electric grids, NASA said Wednesday.

Geomagnetic storms usually last 24 to 48 hours -- but some could last for many days, read a statement from the US National Weather Service.

"Ground to air, ship to shore, short-wave broadcast and amateur radio are vulnerable to disruption during geomagnetic storms. Navigation systems like GPS can also be adversely affected."

NASA's Solar Dynamics Observatory said it saw a large coronal mass ejection (CME) associated with the flash blasting toward Earth at about 560 miles per second (900 kilometers per second).

The flare spread from Active Region 1158 in the sun's southern hemisphere, which had so far lagged behind the northern hemisphere in flash activity. It followed several smaller flares in recent days.

The sun is waking up from a long quiet spell. Last week it sent out the strongest flare for four years – and scientists are warning that earth should prepare for an intense electromagnetic storm that, in the worst case, could be a “global Katrina” costing the world economy $2,000bn.

A solar storm starts with an eruption of super-hot gas travelling out from the sun at speeds of up to 5m miles an hour. Electrically charged particles hit earth’s atmosphere 20 to 30 hours later, causing electromagnetic havoc.

The 11-year cycle of solar activity is quite variable and the present one is running late, with the next maximum expected in 2013.

The peak was not expected to be very strong but that should not cause complacency, said Tom Bogdan, director of the US Space Weather Prediction Center.

lighthouse

March 11th, 2011, 04:58 AM

UPDATE (March 10 @ 1800 UT): Newly-arriving coronagraph data from the Solar and Heliospheric Observatory show no bright CME emerging from this eruption. Some material was surely hurled in our direction, but probably not enough for significant Earth-effects.

After four years without any X-flares, the sun has produced two of the powerful blasts in less than one month: Feb. 15th and March 9th. This continues the recent trend of increasing solar activity, and shows that Solar Cycle 24 is heating up. NOAA forecasters estimate a 5% chance of more X-flares during the next 24 hours.
http://www.spaceweather.com/

lighthouse

March 14th, 2011, 05:25 AM

CAUTIONARY TALE: This week marks t he 22nd anniversary of the Quebec Blackout. On March 13, 1989, a geomagnetic storm brought down Hydro-Québec's power grid and blacked out the entire province. Brownouts and other power irregularities were experienced across much of North America. Today's "smart power grids" are even more vulnerable because they are interconnected by high voltage lines spanning thousands of miles. In good times, this arrangement allows ultilities to guide power wherever it might be needed. During geomagnetic storms, however, it spreads the danger of a blackout far and wide. What we need is a Solar Shield.

WASHINGTON -- An unusual solar flare observed by a NASA space observatory on yesterday could cause some disruptions to satellite communications and power on Earth over the next day or so, officials said.

The potent blast from the sun unleashed a firestorm of radiation on a level not witnessed since 2006, and will likely lead to moderate geomagnetic storm activity today, according to the National Weather Service.

STORM WARNING: NOAA forecasters estimate a greater than 25% chance of geomagnetic storms on June 9th. That's when a CME from the magnificent flare of June 7th is expected to deliver a glancing blow to Earth's magnetic field. High-latitude sky watchers should be alert for auroras.